CBO: Extensions and/or Multi Column Indexes

happy new year to all of you!

I was wondering if it is useful to still have manually created extended statistics (to enhance cardinality calculation for logically connected columns) and multi-column indexes of the same columns at the same time. I need the two- or three-column indexes for query performance reasons anyway, so leaving them out is not an option.

My question is, does it make sense to manually create extended statstics for two columns, that are already part of a two-column index? My field of using this stuff is versions 11.2, 12.1, 12.2 and 18.3 on Linux.

Background: I can't see an extension in dba_stat_extensions if I do not have the extended stats created, so I was thinking, if the CBO can calculate the correct cardinality from the index / index stats, I could spare my stats jobs the effort to calculate many of my virtual column stats.

Thank you in advance, and please don't laugh if I am way off the path... :)

Best regards
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Martin Klier // Performing Databases GmbH Managing Partner // Senior DB Consultant Oracle ACE Director

martin.klier_at_performing-db.com // https://www.performing-databases.com

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http://www.freelists.org/webpage/oracle-l Received on Wed Jan 09 2019 - 11:25:19 CET